The present embodiments relate to acoustic radiation force impulse (ARFI) imaging. By transmitting an ARFI pushing pulse, ultrasound may be used to displace tissue directly or through generation of a shear or longitudinal wave. The displacement resulting from the pushing pulse may be measured using further ultrasound scanning. Elasticity, shear, or other types of parametric imaging measure tissue characteristics based on the displacement caused by the ARFI pulse. Tissue with different characteristics responds to displacement differently.
The ARFI pulse is transmitted as a focused beam. The beam has an hour-glass shape with the narrow portion being at the single focus. The beam shape causes a non-uniform response, resulting in less signal-to-noise ratio for displacements measured in some locations. As a result, a limit range of locations are available for measuring tissue characteristics for a given ARFI pulse. To measure over a range of depths, a rapid sequence of separate ARFI pulses focused at different depths is generated. Laterally, the narrow beam width at the focal point limits the lateral extent to which measurements may be applied. ARFI pulses are repeated to measure displacement at different laterally spaced locations. However, the repetition of ARFI pulses may cause undesired transducer heating and introduces delays in scanning.